linux-ext4 - Re: orphan cleanup on readonly fs will corrupt future fs!

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Date:	Mon, 28 Feb 2011 09:05:30 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Amir Goldstein <amir73il@...il.com>
CC:	Theodore Tso <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Andreas Dilger <adilger@...ger.ca>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: orphan cleanup on readonly fs will corrupt future fs!

On 2/26/11 12:21 PM, Amir Goldstein wrote:
> Hi guys,
> 
> I have just realized something very disturbing -
> that orphan cleanup is not being skipped on readonly mount of ext4/ext3.
> 
> I know that journal recovery is done on readonly mount
> and there is problem with that, since nothing happens
> in the fs level.
> 
> But orphan cleanup deletes inodes and frees blocks and that
> could be very bad for some RO_COMPAT features, SNAPSHOT
> and BIGALLOC to name two.

One thing to note is that if the device itself is readonly,
both journal recovery and orphan processing will be skipped,
if I recall...

-Eric

> I am not so sure why orphan cleanup is so important for readonly
> mount in the first place?
> 
> Now the damage has been done, because current stock kernels will
> corrupt future fs with SNAPSHOT and BIGALLOC features
> (unless Ted backs up from the decision to make BIGALLOC RO_COMPAT...)
> 
> I think that we should skip orphan cleanup on readonly mount ASAP and try
> to push this fix to as many stable/maint kernels out there, before the
> problem gets worse.
> 
> Can anyway see a problem with skipping orphan cleanup?
> Maybe there is a problem with later remount read-write?
> 
> I would spend time more time to investigate these questions,
> but I find this problem too disturbing and urgent to wait until I find
> the time to do so...
> 
> Amir.

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